Ferroelectric memories or ferroelectric random access memories (F-RAM) provide non-volatile data storage through the use of a ferroelectric material which may be polarized in one direction or another in order to store a binary value.
Semiconductor devices, such as integrated circuits (ICs) including FRAM, are fabricated in or on a surface of a semiconductor substrate or wafer that is subsequently divided or diced into a number of discrete chips or dies each having a device or IC formed thereon. One or more dies are then enclosed in a package that provides physical and chemical protection of the die(s) while electrically connecting it with outside circuitry. One common type of package is a molded package in which the die is attached to a flag or die paddle of a lead frame, circuit elements on the die electrically coupled to conductors or lead fingers on the lead frame using a bonding wire, and the die and at least a portion of the lead frame encapsulated in a plastic molding compound using an injection or transfer molding process.
Molded packages provide a number of advantages including a lower per unit cost, and the ability to simultaneously package multiple dies in a sheet or a number of strips, which are subsequently divided to yield individually packaged devices or ICs. However, molded packages also suffer from a number of drawbacks or disadvantages.
In particular, signal margin of F-RAM is affected by the silica fillers (SiO2 particles) in the mold compound of the package. The irregular or round shaped hard silica fillers in the mold compound form high stress points on the F-RAM die and consequently cause clusters of bits in the array showing low signal margin after the mold compound is cured. Polyimide deposited directly on a die has been used to eliminate local stress effects in some semiconductor devices other than those including F-RAM. However, in manufacturing or packaging devices including F-RAM the cure process of the polyimide coating results in a general degradation in signal margin due to an additional thermal budget.